Scalable materials-based solid state actuation is considered to be a critical enabling technology for advanced adaptive and reconfigurable structures, particularly for aerospace applications where scale and weight concerns limit the use of currently available hydraulic and electric systems. The capabilities of an ideal mechanism covering this implementation include simultaneous high-strain (>100%) at substantial loads (>10 MPa), and a stiffness modulus approaching that of the surrounding structure (>10 Gpa). Additional capabilities emerge if the material can be activated at low voltage, high temperatures (>150 degrees C.) and maintain its geometry when power is removed to exhibit “zero power hold.”
Many solid state actuation technologies based on a variety of mechanisms are currently under development. Each material system exhibits a set of properties and actuation characteristics (strain, force, speed, actuation type, etc.) that yield suitability to specific applications.
Electrochemically-actuated material systems have emerged as promising candidates to cover a range of high-strain/high-force implementations. Polymer-based electrochemical systems have been the primary focus to-date with the majority of attention devoted to ionic polymer metal composites, or IPMCs, and conducting polymers. Recent advances in the performance of these materials have been impressive with strains to 15% and work densities above 80 kJ/m3 for some combinations. The low voltage, light weight and potential low cost of these materials are attractive when considering large system integration.
Other polymers, specifically dielectric elastomers, show extremely large strains (>100%) at high rates with potentially high energy densities (up to 3.8 MJ/m3) when subjected to strong electric fields (>100 MV/m).
Current research in the area of carbon-based active materials suggests material systems that are structurally stiff, but capable of relatively small strains when activated. By using double layer charge injection to increase the C—C bond length in carbon nanotubes, strains on the order of 0.1–0.2% and stresses in the MPa range have been demonstrated in carbon nanotube papers. Carbon nanotube-based actuators could deliver strain of >1% and stress outputs of hundreds of MPa.